It has to do with your nerves, surprisingly.

After a long bath or swim session, you've probably seen the pads of your fingers get wrinkly. While they return to normal soon after you leave the water, you can't help but wonder what's with the raisin-like look in the first place?

YouTube channel SciShow has revealed the answer. At first, scientists believed osmosis caused fingers and toes to look like that. "The influx of water, they thought, expanded the skin's surface area, but not the tissue below it, creating a puckered effect," reports Metro.

That thinking changed in 1935 after doctors observed patients with nerve damage. One of them, for example, had nerve damage on three of his fingers. The undamaged fingers crinkled up when exposed to water while the damaged ones remained unwrinkled. Their conclusion: It's the nervous system that causes your digits to look like prunes. As the video puts it, "The nervous system causes the wrinkling by constricting blood vessels below the skin which causes the upper layers of skin to pucker."

Biologists also think that evolution has something do with it. Our ancestors dealt with rainy conditions and needed a stronger grip to work efficiently. In a recent study, researchers saw that theory in action as they discovered that people with wrinkly fingers were able to grab wet items 12% better. Fascinating!

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